Method and apparatus for cooling the flame of an industrial gas burner

ABSTRACT

A method of cooling the flame of an industrial burner for gaseous fuel in which a gas burner is used having a ring-shaped gas-outflow opening and a flow of atomized water is sprayed from the centre of the burner mouth substantially axially into the annular flame burning at the gas-outflow opening.

United States Patent 1191 Varekamp [11] 7 3,809,523 1451 May 7,1974

[22] Filed:

[ METHOD AND APPARATUS FOR COOLING THE FLAME OF AN INDUSTRIAL GAS BURNER [75] Inventor: Willem Varekamp,Soest,

Netherlands [73] Assignee: Ingenieursbureau Rodehuis &

Verloop N.V.

Sept. 1, 1972 21 Appl. 196.: 285,857

[30] Foreign Application Priority Data Jan. 6, 1971 Netherlands 7100208 [52] U.S. Cl 431/4, 431/190, 60/DIG. 11

511 1111. C1 F23j 7/00 [58] Field of Search 431/4, 190, 187

[56] References Cited UNITED STATES PATENTS Harslem 60/3955 1/1973 -Berlyn 60/3955 x 2,140,085 12/1938 Maina 60/DIG. 11

3,162,236 12/1964 Williams 1 431 4 x 3,342,242 9/1967 Verloop 431/187 3,133,731 5 1964 Reed 431/187 x 2,761,496 9 1956 Verner et al 431/4 x FOREIGN PATENTS OR APPLICATIONS 596,097 7/1959 ltaly 431/187 Primary ExaminerWilliam F. ODea Assistant ExaminerWil1iam C. Anderson Attorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen [57] ABSTRACT A method of cooling the flame of an industrial burner for gaseous fuel in which a gas burner is used having a ring-shaped gas-outflow opening and a flow of atomized water is sprayed from the centre of the burner mouth substantially axially into the annular flame burning at the gas-outflow openingv 5 Claims, 1 Drawing Figure PATENTED HAY 7 I974 wmmm mmOm BACKGROUND OF THE INVENTION The invention relates to a method of cooling the flame of an industrial burner and more particularly to of such a burner for gaseous fuel. The invention also relates to a burner assembly for carrying out the method.

It is known that in the operation of, for instance, industrial gas burners high flame temperatures lead to the forming of nitric oxides which are harmful to the environment. For this reason, attempts have been made to reduce the normal temperature of l,700 to 1,800C occuring in natural gas flames to below the critical borderline temperature of approximately l,300C which is critical to the development of such nitric oxides.

SUMMARY OF THE INVENTION The invention has for its object to provide a method for cooling the flame of an industrial gas burner allowing the control of the reduced flame temperature in a simple andefficient manner.

Another object of the invention is to provide a gas burner assembly of simple design suitable for carrying out the above-mentioned method by making it possible to effectively reduce and control the temperature of the flame formed at the mouth of the burner by the combustion of the gas flowing-out therefrom.

According to the invention, a burner is used which forms an annular outflow of gas at the mouth of the burner so as to generate an annular flame by the combustion of the gas, and a flow of atomized water is continuously sprayed from the center of the burner mouth substantially axially into this annular flame.

As a result, the annular flame is cooled directly as it occurs by means of the water sprayed into its center this spray completely evaporating over a very short path, i.e., within the length of the flame. In this way there is no danger that the flame becomes unstable-or is extinguished by the spraying in of water as the secondary combustion air can continue to flow-in undisturbed on the outer side of the burner towards the annular flame.

Preferably, the water is atomized with the help of an air stream. This atomizing air consequently supplies at the same time primary combustion air within the annular flame.

The extent of the cooling of the flame can be controlled and regulated quite simply-by controlling the amount of atomized water which is supplied. When burning natural gas, the amount of water supplied is preferably about 1 kg water per m of burned gas.

In accordance with a further advantageous feature of the invention. waste waters containing impurities can also be sprayed into the 'burner flame. In that case,

apart from the desired cooling of the flame, also waste materials which can cause environmental damage when drained in outside water can be rendered harmless by combustion. I

A particularly suitable burner assembly for carrying out the above described method is the one described in my British Pat. Specification 1,080,528. This burner assembly has a gas burner with a substantially cylindrical twin-walled casing for the supply of gas to a ringshaped burner mouth, and a liquid atomizing device mounted in the center of the cylindrical casing with a central liquid supply conduit and at least one atomizing air conduit for connection to a source of compressed air and provided with means for producing turbulence of the air. In this known burner assembly the liquid atomizing device forms an oil burner so that this assembly can be operated as required with gas and/or oil. In accordance with the concept of the present invention, however, the liquid supply conduit of the liquid atomizing device is connected to a source of water under pressure.

In this way, during operation of the gas burner of this burner assembly, by means of the liquid atomizing device centrally arranged therein a water mist finely atomized by the atomizing air is sprayed into the center of the flame.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing shows, by way of example, an axial section of an embodiment of a burner assembly for carrying out the method according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The drawing represents an axial section through one of the burner assemblies of a boiler which, in a known manner, is fitted with several burners.

The boiler has a combustion chamber 1 with a furnace wall 2 on which are mounted boiler tubes 3 and a boiler wall insulation 4, as is shown diagrammetrically in the drawing. The furnace wall has a number of flame holes such as 5 each with a similar burner assembly 6 mounted therebehind, only one of which is represented in the drawing.

This burner assembly 6 is fitted for the combustion of gaseous fuels such as natural gas, the gas emerging in the form of a ring from out of the mouth of the burner. For the rest, the burner can be designed in any suitable known manner. In the example represented in the drawing, the burner assembly is of the type as described in my British Pat. Specification No. 1,080,528 which assembly comprises a substantially cylindrical gas burner with a fluid atomizing device housed at its center. The gas burner has a twin-walled cylindrical casing with an outer wall 7 and an inner wall 8 which form a ring-shaped gas supply channel 9 into which natural gas or any other suitable gaseous fuel can be supplied via a gas supply conduit 10 which is, connected to the rear end of the outer wall 7 and extends rearwards. At the front end the two walls 7 and 8 run conically inwards to a conical front wall 11 which closes the channel 9 and which is provided with a circular row of narrow gas-outflow bores 12. A forwardly extending coneshaped flame funnel 13 is attached to this front wall 11. Immediately behind this funnel 13 a circular row of gas outflow tubes 14 is screwed in the end portion of the outer wall 7, which runs obliquely inwards, the axes of these tubes lying on a conical surface parallel to the generatrices of the funnel 13. An air-deflecting bushing 15 is attached in any suitable manner behind the funnel to the outside of the casing wall 7, and extends on the front side in accordance with the shape of the funnel 13 in a conical manner, its rearward part being similarly conically extended. Thereby an annular air channel 16 is formed between the wall 8 of the casing with the flame funnel 13 attached thereto and this air-deflecting bushing 15, which air channel 16 has a constricted middle portion and through which channel secondarycombustion air is conducted towards and along the gas outflow tubes 14 in a way'which will be further described later.

A fluid atomizing device 17 is mounted in the. gas burner casing 7, 8 and cancorrespond in terms of its design to an oil burnerof suitable known type. In the embodiment represented, the oil burner used corresponds in design to that disclosed in my published Dutch Pat. application No. 270,257 and provides a two-stage atomization of the liquid by means of primary atomizing air of higher pressure than the secondary combustion air. The device 17 has a liquid supply tube 18 running axially through the middle of the casing 7, 8 and connected at its rear end via a coupling 20 carrying a liquid pressure measuring gauge 19 to a flexible feedconduit 21. The atomizing air is supplied through a channel enclosed by the inner wall 8 of the casing, a lateral connecting member 22 being con-' nected to this casing wall 8 at the rear end thereof for connection with a source of compressed air at constant pressure.

The burner assembly 6 lies with its burner mouth in the middle of the circular flame hole 5 and extends rearwards through a wind box 23 which is common to the several burners and which is formed between the furnace wall 2 and an outer wall 24. This wind box.

supplies the necessary secondary combustion air by natural draft or with the help of a fan in conventional manner. The outer wall 24 ofthe wind box has an aperture 25 which is sealed off by a removably fixed front plate 26 of the burner assembly; This front plate 26 supports the outer burner case wall 7 by means of a bushing 27 and reinforcement plates 28 in'a way whichis not shown in detail, while the gas supply conduit 10, the liquid supply tube 1 8, andthe inner wall 8 of the casing with the atomizing air connection 22 are sealingly led outwards through this front plate 26 and a dome-shaped member 29 attached thereto.

As described in my above mentioned Dutch Pat. application No. 270,257, the liquidatomizing device 17 has a cylindrical casing 30 fitted in the inner casing wall 8 and comprising a supporting ring 31 held by a number of radial arms. The ring 31 supports a dividing bushing 32 arranged coaxially in the casing 30 and supporting a conical member 33 at its front side. This conical member 33 encloses a mixing chamber 34 and joins at its rear edge the forward edge of a bushing-shaped spraying-head holder 35 which envelops with its rear end the front end of the liquid supply tube 18 and which supports a spraying head 36 having a number of obliquely outward-facing spraying apertures. The spraying-head holder 35 has a number of slot-like air inlet ports 37 which discharge tangentially into the mixing chamber 34, this holder thus forming a vortex sleeve.

The supporting ring 31 also carries a second vortex sleeve 28 which surrounds the dividing bushing 32 with play, and which has a conical thickening at its front'end connected to the front edge of the casing 30. The sleeve 38 is likewise provided with a number of slot-like air inlet ports 39, which run in a tangential direction in opposition to the slot-like ports 37 in the spraying head holder 35; In this way, the atomizing air which is led axially through the inner cylindrical wall 8 of the casing is divided into two streams, one air stream flowing through the space between the dividing bushing 32 and the liquid supply tube 18 to the slots 37 and emerging under entrainment of the liquid discharged by the spraying head 36 into the mixing chamber 34 with pronounced turbulence. The other atomizing air stream flows through the space between the casing 30 and the vortex sleeve 38 and passes through the slots 39 of this sleeve, with pronounced turbulence, into the annular space between the vortex sleeve 38 and the dividing bushing 32. This second air stream, upon leaving this latter space, meets the .atomizing cone whirling in the opposite direction and emerging from the mixing chamber 34. As a result of the air streams with opposite vortex flow meeting each other, a pronounced turbulence occurs so that the liquid which is carried along is finely distributed and uniformly mixed with all of the emerging atomizing air.

The feed conduit 21 is connected via a regulating valve 40 to a source 'of water under pressure.

In the operation of the burner assembly described above, natural gas is fed into the gas supply conduit 10, while the valve 40 is opened. The secondary combustion air emerging from the wind box 23 flows along the burner assembly 6 through the flame hole 5 into the combustion chamber, part of the air flowing along the outer wall 7 of the burner casing and passing through the ring-shaped channel 16 within the air-deflecting bushing 15 to deliver mixing air for the gas flowing out of the gas outflow tubes 14. The resulting gas/air mixture is then mixed again with the rest of the secondary combustion air flowing through the aperture 5 whereby an annular flame is formed at the burner mouth. Atomized water emerges from the mouth of the liquid atomizing device 17 and is intimately mixed with the atomizing air fedto this device in the above described manner which water spray thus cools the annular flame from the inside. Gas also passes through the narrow gas outflow bores 12 into the space within the flame funnel 13, which gas is kept in a state of combustion by means of the supplied atomizing air and forms a constant stable ring-shaped sustaining flame for the annular main flame.

By suitable adjustment of the regulating valve 40, the rate of supply of water can be controlled so that the desired cooling of the flame is achieved. In general 1 kg water per in of combusted natural gas will be supplied. The spray-of atomized water emerging from the mouth of the liquid atomizing device 17 cools the flame directly at the. point where it is formed and evaporates over a very short path which is at least shorter than the length of the flame. The flame is thus cooled in a uniform manner over its whole periphery by means of the central supply of this atomized water and the gas burns in a stable manner within a large range of adjustment since the secondary combustion air flowing along the outside of the burner assembly can feed the flame continuously and unimpeded by the water spray.

What is claimed is: 1.

1. A method of cooling the flame of an industrial gas burner for the furnace of a boiler, said method comprising forming an annular outflow of gas at the mouth I of the burner so as to generate an annular flame by the combustion of said gas, feeding combustion air to said flame circumferentially therearound, and continuously spraying a flow of atomized water from the center of the mouth of the burner separately and, distinct from i the gas outflow substantially axially and directly into the center of said annular flame so providing that the annular flame burning at said burner mouth is fed circumferentially with combustion air on its outer side and is cooled at its inner side by said streams of atomized water.

2. The method of claim 1 in which the water is atomized by a stream of air.

3. The method of claim 1 in which water containing impurities is sprayed into the flame.

4. A gas burner assembly for use in the furnace of a boiler, said assembly comprising a gas burner having a burner mouth with a ring-shaped gas-outflow opening, annular gas conduit means for supplying gaseous fuel to said burner gas-outflow opening, means for guiding combustion air to said burner mouth circumferentially therearound, means for atomizing liquid mounted coaxially within said annular gas conduit means at said burner mouth and having a liquid discharge opening in at least one atomizing air conduit for connection to a source of compressed air, said air conduit being provided with means for producing turbulence of the air passing therethrough. 

2. The method of claim 1 in which the water is atomized by a stream of air.
 3. The method of claim 1 in which water containing impurities is sprayed into the flame.
 4. A gas burner assembly for use in the furnace of a boiler, said assembly comprising a gas burner having a burner mouth with a ring-shaped gas-outflow opening, annular gas conduit means for supplying gaseous fuel to said burner gas-outflow opening, means for guiding combustion air to said burner mouth circumferentially therearound, means for atomizing liquid mounted coaxially within said annular gas conduit means at said burner mouth and having a liquid discharge opening in the center of said ring-shaped gas-outflow opening, and a source of water under pressure connected to the liquid atomizing means, such that the annular flame burning at said burner mouth is fed circumferentially with combustion air on its outer side and is cooled at its inner side by a stream of atomized water discharged at said liquid discharge opening.
 5. The assembly of claim 4 in which said liquid atomizing means includes a central liquid supply conduit connected to said source of water under pressure and at least one atomizing air conduit for connection to a source of compressed air, said air conduit being provided with means for producing turbulence of the air passing therethrough. 